EVOH resin has a crystal part by firmly hydrogen bonding between hydroxyl groups of the molecular chains thereof. Oxygen in atmosphere is prohibited to intrude into the crystal part and therefore EVOH resin can exhibit excellent oxygen barrier performance and other gas-barrier performance. This makes EVOH resin layer utilize a gas-barrier layer of a multilayered film for packaging for food and so on. However, it is known that the gas-barrier performance is deteriorated when a package with a multilayered film employing EVOH resin layer as a gas-barrier layer is subjected to a treatment with hot water for long hours like a retorting treatment. This is supposed that the hot water treatment introduces water into an EVOH resin layer from edges of the multilayered film and thereby breaking hydrogen bonds formed in the EVOH resin molecules, as a result, oxygen in atmosphere could easily intrude into the EVOH resin layer.
It is known that addition of hydrate-formable alkaline earth metal salt as a drying agent to an EVOH resin is useful for avoiding the deterioration of gas-barrier performance caused from a hot water treatment. For example JP2010-59418A (patent document 1) suggests a resin composition comprising an EVOH resin, a partially or completely dehydrated carboxylate hydrate. The patent document 1 discloses that addition of dehydrated disodium succinate hydrate helps retain excellent gas-barrier performance after a hot water treatment.
Partially or completely dehydrated carboxylate hydrate can contain water molecules as crystallization water. Therefore, the moisture entering into an EVOH resin layer during a hot water treatment would be absorbed as crystallization water, which could avoid EVOH resin from breaking hydrogen bonds as well as deteriorating the gas-barrier performance.
In addition, JP2011-225800A (patent document 2) suggests an EVOH resin composition containing a partially or completely dehydrated polyvalent metal sulfate hydrate as a drying agent for not only retaining gas-barrier performance after a hot water treatment but also improving melt-kneading property of EVOH resin. The patent document 2 discloses that a resin composition containing a partially or completely dehydrated magnesium sulfate hydrate still exhibited more excellent gas-barrier performance after a hot water treatment than that containing alkaline metal salt sulfate as shown in Table 1, and that the former exhibited more stable melt viscosity behavior than a resin composition containing metal salt carboxylate as shown in Table 3.